Vulcanizable mixture of thermoplastic interpolymers



Patented Nov. 23, 1948 VULCANIZABLE MIXTURE OF THERMO- PLASTIC INTERPOLYMEBS George William Stanton and Charles Everett Lowry, Midland, Mich" asllgnors to The Dow Chemical Company, Midland, Mieln, a corner ration of Delaware No Dra This invention relates to a composition of matter comprising particular proportions of each of two types of thermosplastic polymeric materials, which composition is vulcanizable to produce a rubber-like product having the properties desired in shoe soles.

A synthetic, rubber-like vulcanized composition, to be satisfactory for use in shoe soles, should be able to meet'each of several physical standards. Thus, when subjected to a standard abrasion test, it should be reduced in thickness less than 0.0025 inch (2.5 mils) and should lose less than 10 milligrams weight per square inch of abrased surface for each 1,000 revolutions of a standard abrasive wheel applied thereto. It'

should have a tensile streng-h of at least 550 pounds per square inch and should not becapable of much morethan 400 percent elongation. It should withstand at least 5,000 bends about 1 inch mandrel at room temperature'and should not break when bent 180 over such a mandrel after having been held at F. for 12 hours. In

thicknesses of inch. a pull of at least 30 pounds should be required to cause a stitch to tear through the sole when dry, and a pull of at least 25 pounds should be required when wet. Most of Application July-semi, Serial No. 104,24:

4 Claims. (Cl. 260-45.!)

. 2 Y per cent of butadiene, and (3) from 0 to 60 per cent of a compound copolymerizable with the vinylidene chloride and butadiene, containing a single ethylenic double bond in its monomeric molecule and capable of forming by itself a thermoplastic polymer. The preferred: (B) constituent is the binary interpolymer of from 50 to 85 per cent of vinylidene chloride and from 50 to per centof butadiene. The preferred mixture with one another in all proportions, but mixtures ent purpose. Those with too little (A) are too hard and too brittle at low temperatures, when vulcanized, and those with too little (B) do not vulcanize readily, if at all, and are too soft. The two interpolymers are mixed, before vulcanization, by any of the usual mixing procedures. They may be mixed together on a multiple roll mill, either cold or hot, or they may be mixed in a lated object is the provision of a satisfactory vulcanized synthetic shoe sole.

The invention, whereby the foregoing objects,

are realized, resides in the discovery of a composition of matter containing (A) from 10 to 67 per cent by weight of the thermoplastic interpolymer produced by polymerizing styrene while in aqueous emulsion at a temperature above 50 C. and then adding monomeric butadiene to the emulsion of substantially fully polymerized styrene and polymerizing the butadiene while dispersed in the emulsion at a temperature above 50 C., in proportions such that the final interpolymer contains from 20 to 80, and preferably weight of vinylidene chloride, (2) from 15 to 50 erator, and an activator, and

two constituents, and precipitating together the I mixed dispersed solids,

Any of the usual vulcanizing agents and mixtures may be used. One typical and satisfactory formulation comprises, for each parts by weight of the (B) constituent, about 1 part of stearic acid, about 10 parts of dibutyl phthalate, about 5 parts of litharge, about 1 part of benzothiazyl disulfide, and about 2 parts of sulfur. There may be used, as well, with this or other typical formulations, minor amounts of waxes, reinforcing pigments and fillers, as will be illustrated in the examples. The mixture of agents used will include, in each case, sulfur, an accelwill usually include a plasticizer.

Satisfactory vulcanization and cure is obtained in from 20 to 90 minutes at a temperature in the range from to C. vulcanization is preferably effected while the compounded slabs are confined under a pressure of from 400 to 1,000 pounds per square inch.

- 3 The following examples illustrate the practice of the invention:

Exam 1 A series, of compositions was prepared containing:

(A) Constituent--35 per cent styrene, 65 per cent butadiene-variable amounts as shown in Table I.

4 Abrasion index, mils reduction in thickness per 1,000 revolutions of a standard abraflexing-appearance after 5,000 flexes at room temperature-no cracks. Cold flex-bent over 1 inch mandrel after condi- (B) Constituent-70 per cent vinylidene chlotioning overnight at 0 F.no cracks.

ride 30 per cent butadifmkmo parts Similar tests run on all of the cured compositions Parts show that each oi them meets or exceeds the Stearic 'acidlubrlcant 1 established requirements for shoe soles. Dibutyl phthalate-plasticizer or softener--- mmpmz Magnesium oxide-activator;a 5 sulfun-vulcanizeir 2 In a manner similar to that reported in Ex- Benzothiazyl disulfide-accelerator 1 a p e a se ies o commeitlonswas p p Finely divided hydrated calcium silicate-fillercontaining:

variable amounts as shown in Table I. no (I Parts The (Blconstituent was broken down on a cold A) g per styrene' mill and the soften r and lubricant (A) conper but 33 (B) Constituent--55 per cent vinylidene chlostituent, activator, vulcanizer, accelerator and ride, 30 per cent butadiene, per cent reinforcing filler were added in the order given. other polymeflzable compound listed Sometimes the (A) constituent was divided in Steam: acid two parts, and one of these was added and worked mbutyl aggig m in on a hot mill after all other agents had been uthar 5 added. The mix was sheeted from the mill and. i a' 'i" g hg 1 cut into pieces of appropriate size which were Sulfur '7 2 then cured atv 138 C. for the indicamd time, in minutes, and under a pressure of 750 pounds The mixing and vulcanlzing procedure was that per square inch. The cured vulcanized slabs reported in the prior example. Results of physiwere subjected to a number of tests, with recal tests on the vulcanized sheets are given in suits as shown in the table. The low temperature Table H,

Table lZ Tensile Stress Permanent sm r r nffi gag fit; stitttt, tifiit? 55g; fli

Minutes lbs/sq. in. Per Cent Per Hardness 100% 300% Elong. Elong.

00 010 s10 as m 120 40 1,015 410 10 02 s 05s 1,280 430 14 02 300 815 20 7:10 370 a 04 250 500 40 710 380 10 04 215 s90 40 1, no 440 32 74 3110 s25 1,115 s 16 0a 325 885 00 1, 050 420 is 04 230 080 brittle point of each composition was below The vulcanized sheets were also tested for abra- 60 C. sion resistence, and found to compare favorably Table I Pounds Per Permanent 7 121%? ri ls A 011 0 'r El 1 3 Cons lm- Sl li a t Tl strzfi tii. to l fi' l B 3; 35

' ent,Perts Parts Min. lbs./sq.in percent fig Hardness 300% Elong. Elong 1 15 so 900 330 24 00 050 070 2 so 15 00 1,140 3:10 20 00 1,100 a s0 15 so ,220 300 24 00 715 220 4 100 so 20 000 350 2s 82 4110 010 s 100 110 so 350 380 :14 as 400 710 e 20o 20 000 220 20 as 4110 1 200 so 840 350 40 114 465 780 s 200 so 20 810 300 40 as 810 9 200 so so 030 210 so 02 also Several sole slabs from batch No. 2, reported 70 with the compositions of Table I, and to be genln the table, were submitted to shoe manufacerally superior in this regard to commercial shoe turers for further specific tests. The reports insoles made of synthetic rubber-like interpolydicate a confirmation of the physical properties mers of styrene and butadiene, of the type known listed in thetable and give the following addiuniversally as GR-S rubber. These sheets also tional data: I 78 pass the previously described flexing tests, both at room temperature and after conditioning at sub-zero temperatures. The stitch tear strengths of the various sheets have diverse values, but all are above the recommended 30 pounds (dry) and 25 pounds (wet).

Example 3 Q A particularly desirable shoe sole composition has been developed comprising the following constituents:

when vulcanized-in sheet form, this composition was tested in comparison with two commercial synthetic rubber-like shoe soles. The results are given in Table III.

Table III Composi- Commer Commertion oi cial Bole eisl Bole Example 3 X Y'.'

Hardness (Durometer A):

Top 00 95 80 Bottom 90 82 80 Tensile strength, pounds per square inch 1,700 1, 100 i; 300 Set, at break 44 40 Density 1.25 1.21 1.19 Abrasion index (see Note) 5. 7 8.3 9.0

N our-Abrasion index is reported in this example as the number oi milligrams lost per thousand revolutions oi a standard abrasive wheel under a standard load on a Taber abraser, per square inch of abrssed surface.

1 Not determined.

In a manner similar to that reported in Ex ample 2, compositions according to the present invention were prepared and vulcanized, in which the (A) constituent contained from 20 to 80 per cent of prepolymerized styrene and correspondingly from 80 to 20 per cent of after-polymerized butadiene and the (B) constituent contained, in addition to the previously defined proportions of (1) vinylidene chloride and (2) butadiene. vary-,

ing amounts from nil up to 60 per cent of (3) a polymerizable compound, such' as those listed in Example 2, containing a single ethylenic double bond in its monomeric molecule and capable of forming by itself a thermoplastic polymer. Each of these vulcanized compositions, when in sheet form, had the properties desired in synthetic shoe soles, and, while the compositions varied among themselves in particular properties, they were all superior to the individual interpolymers from which they were made and were at least comparable with the available commercial synthetic sole materials.

It is desired that a vulcanized shoe sole be relatively dead" and inelastic so that, among other reasons, it will not tend to spring away from and be cut by the sole stitching. A laboratory test which gives an index of this property is the "Bashore Rebound" test. High values indicate elastic materials, and low values indicate inelastic ones. The Bashore rebound values of vulcanized shoe soles made from the common synthetic rubber known as GR-S are in the range from to 80, while those of soles made in accordance with the present invention are in the range from 10 to 20.

Shoe soles made of the various compositions specifically described in the examples, as well as of other compositions falling within the present invention, have been subjected to use on cement iloors and have shown negligible signs of wear in 3 months. Prolonged tests indicate an expected life of a year or more.

The compositions of the present invention are not limited to use as shoe soles, but their combination of properties makes them especially desirable for such use.

-We claim:

1. A vulcanizate of a mixture of ,(A) from 10 to 6'7 per cent by weight of the thermoplastic interpolymer produced by polymerizing styrene while in aqueous emulsion, at a temperature above 50 C. and then adding monomeric butadiene to the emulsion of substantially fully polymerized styrene and polymerizing the butadiene while dispersed in the emulsion at a temperature above 50 C., in proportions such that the final interpolymer contains from 20 to 80 per cent of styrene interpolymerized with from 80 to 20 per cent of butadiene, and (B) correspondingly from 90 to 33 per cent by weight of the interpolymer of (1) from 25 to 85 per cent oi vinylidene chloride, (2) from 15 to 50 per cent of butadiene, and (3) up to per cent of a compound copolymerizable with the vinylidene chloride and butadiene, containing a single ethylenic double bond in its monomeric molecule and capable of forming by itself a thermoplastic polymer. 1

2.. A shoe sole composed of the vulcanizate claimed in claim 1.

3. A vulcanizate of a mixture of (A) from 10 to 67 per cent by weight of the thermoplastic interpolymer produced by polymerizing styrene while in aqueous emulsion, at a temperature above 50 C. and then adding monomeric butadiene to the emulsionoi substantially fully polymerized styrene and polymerizing the butadiene while dispersed in the emulsion at a temperature above 50 C. in proportions such that the ilnal interpolymer contains from 85 to 45 per cent of styrene interpolymerized with irom to 55 per cent oi butadiene, and (B) correspondingly from 90 to 33 per cent by weight of the interpolymer of from 50 to per cent of vinylidene chloride and from 50 to 15 per cent oi butadiene.

4. A shoe sole composed of the vulcanizate claimed in claim 3.

GEORGE WILLIAM STANTON. CHARLES EVERE'I'I LOWRY.

No references cited. 

